I definitely recommend booking a tour of Halong Bay.
We booked a 3 day/2 nights tour for 125$ per person in 2017 with “Golden Bay Cruise“ (the boat company). The tour was fine, time on the boat definitely the best ever, evening squid fishing and some kayaking.
The second day is a must for those who want to visit Monkey Island (beautiful beach and some monkeys lurking around, searching for food to steal). Otherwise the rest of the afternoon is spent on the Island where the second night’s hotel is and unless you organise something yourself, that time is pretty much wasted.
On the last day and on the way back to Halong, you get a very basic cooking lesson on how to wrap spring rolls, a boring 2-hour wait at the port and the bus ride back to your hostel.
During our night on the boat it started raining. We were pretty lucky because we had finished our daily activities and even the night fishing session but we did not expect what happened later in the night…
Aron woke me up in the middle of the night and the roof was leaking on my feet. I had not felt it because it had not gone through our sheets yet but it was raining on our bed! It was not a little drip, it was a full shower!
So of course I went to get a member of the crew… They spent 1h trying to move the beds so that it would not drop on the bed and when that failed they nailed a holy thick plastic sheet to the roof. In the morning it was leaking again through one of the holes…